1 Field of the Invention
The present invention relates to an exposing apparatus and more particularly, it relates to an exposing apparatus used in the course of manufacturing shadow masks for color picture tubes.
2 Description of the Related Art
It is needed in the course of manufacturing shadow masks for color picture tubes that an iron plate 1 is selectively etched by acid on both sides thereof to accurately form a plurality of apertures 2 which pass through the iron plate 1, as shown in FIG. 1.
These apertures 2 are formed as follows. As shown in FIG. 2, photosensitive material is coated on both sides of the iron plate 1, which is then closely held between a first glass mask plate 6 on the inner side of which a large aperture pattern 4 is drawn and a second glass mask plate 7 on the inner side of which small aperture pattern 5 is drawn. Both sides of the iron plate 1 is irradiated by ultraviolet rays shot from a mercury-vapor lamp through the glass mask plates 6 and 7 to expose the photosensitive material on both sides of the iron plate 1. The photosensitive material on both sides of the iron plate 1 is developed, that is, that portion of the photosensitive material which is not exposed is removed from both sides of the iron plate 1 to form etching resistive patterns thereon. Using these etching resistive patterns as masks, the iron plate 1 is etched by acid to form a plurality of apertures 2 which pass through the iron plate 1.
When the large aperture pattern 4 is shifted from the small aperture pattern 5 upon the exposing step in the above-described process, the apertures, which are formed by etching the iron plate 1 with acid using the aperture patterns 4, 5 as etching masks, cannot have their predetermined shapes and sizes, or they cannot be passed through the iron plate 1 in the worst case.
In order to prevent this, the two glass mask plates 6 and 7 were opposed to each other without interposing the iron plate 1 between them to find by eyes whether or not they were aligned with each other. When they were not aligned with each other, one of them was moved to become aligned with the other.
However, this method of aligning the glass mask plates 6 and 7 with each other had the following problems.
In the case of the exposing apparatus used to make shadow masks for color picture tubes, the long iron plate 1 wound round drums 8 and fed, as shown in FIGS. 3 and 4, is repeatedly exposed in the manner as shown in a flow chart in FIG. 5. When the iron plate 1 is once interposed between the glass mask plates 6 and 7, therefore, it cannot be found by eyes whether or not the positional shift of one glass mask plate relative to the other is caused.
Further, the exposing step is repeated about 700 times in one or two days to expose all of the iron plate 1 wound round the drums 8. When the iron plate 1 is once interposed between the glass mask plates 6 and 7, therefore, the positional shift cannot be confirmed by eyes on the way of the course of repeating the exposing step even if this positional shift of one glass mask plate relative to the other is caused. This may lead to plenty of inferior products.